The development of muscles.

The muscles of the body should be considered in terms of their development and function, as well as the topography of the systems and groups to which they are added.

The muscles of the body develop from overlies the sides of the chord and the brain tube dorsal part of the mesoderm, which is divided into primary segments or somites. After selecting skelerotoma going to education of the spinal column, the remaining part of the dorsomedialnaya somite forms miotomWhose cells (myoblasts) are extended in the longitudinal direction and merge with each other and become in the future in symplasts muscle fibers. Part of myoblasts differentiated into specific cells - miosatellity lying next to Symplast. Myotomes grow in the ventral direction and divided into dorsal and ventral parts. From the dorsal part of the myotomes occurs dorsal (dorsal) muscles of the trunk, and from the ventral - muscles, located on the front and side of the trunk and called ventral (Fig. 66, 67).

Each miotom (Myomere) soimennogo grow into branches of spinal nerve (nevromera). Accordingly, the division of the myotomes in 2 parts of the nerve Waste 2 branches, of which the dorsal (back) part of the dorsal part of the myotomes, and ventral (front) - in the ventral. All originate from the same myotomes muscles supplied by the same spinal nerve. Nearby myotomes can coalesce with each other, but each of intergrown myotomes keeps referring to his nerve. Therefore, the muscles originating from several myotomes (eg, the rectus abdominis muscle), are innervated by several nerves. Originally myotomes on each side separated by a transverse connective tissue septa, myosepta (Fig. 68). Such a segmented arrangement of trunk muscles in the lower animals is a lifetime. The higher the same pozvonoch.yh and humans due to a greater differentiation of muscle mass segmentation is much smoother, although traces of it and remain in the dorsal (short muscles are thrown between the vertebrae), and in the ventral muscles (intercostal muscles and the rectus abdominis muscle). Part of the muscles that developed on the body, remains in place, forming a local, autochthonous musculature (autos - the same, chthon, Greek. - land). Another part of the development process moves from the trunk to the extremities. These muscles are called trunkofugalnymi (truncus - trunk, torso, fugo - rout). Finally, the third part of the muscle, which arose on the extremities, moves to the trunk. It trunkopetalpye muscle (yard - aspire). Based on the innervation is always possible to distinguish autochthonous (ie, developing in a given location) from the muscle gurus moved to this area of other muscle-alien

The musculature of the extremities formed from the mesenchyme of limbs and kidney receives its nerves from the anterior branches of spinal nerves through the brachial and lumbosacral plexus. In lower fish (villages) of the myotomes of the trunk muscles grow buds, which are divided into two layers, located on the dorsal and ventral sides of the skeleton of the fin. Similarly, at the vertebrate muscle in relation to the rudiment of the skeleton limbs initially located dorsal and ventral (extensors and flexors). With further differentiation of the rudiments of the forelimb muscles grow and in the proximal direction (trunkopetalnye muscle) and cover the autochthonous muscles of the torso from chest and back (mm. pectorales major et minor, m. latissimus dorsi). In addition to this primary muscles of the forelimb to the upper extremity are added trunkofugalnye muscles, ie, derivatives of the ventral muscles. employees for moving and fixing the belt and move it from the head (mm. trapezius and sternocleidomastoideus) and trunk (mm. rhomboideus, levator scapulae, serratus anterior, subclavius, omohyoideus). Y belt hind limb muscles of the secondary does not develop, as it still connected to the spine. The complex differentiation of the limbs of terrestrial vertebrates, especially in the higher forms, explains the function of limbs, into complex instruments that perform various kinds of motion.

Muscles of the head arise partly from the head somites, but mainly from the mesoderm gill arches. Visceral apparatus in the lower fish sostoig of solid muscle layer (total constrictor), Divided by its innervation of specific areas, coinciding with the meta-dimensional arrangement of the gill arches: 1 st gill (inferior alveolar) arc corresponds to pair of cranial nerves V (trigeminal nerve), 2 nd gill (hyoid) arch - VII pair (front nerve), the 3rd gill arch - IX pair (yazykog stalls nerve). Remainder of the total constrictor supplied a pair of branches X (vagus nerve). Behind the general constrictor segregated beam that attach to the upper extremity (trapezius muscle). When the transition from water to land in lower vertebrates stopped breathing gill-adapted for life in water, muscles gill apparatus (visceral) spread to the skull, which turned into chewing and facial muscles, but retained his connection with those parts of the skeleton, which arose from gill arches. Therefore, the chewing muscles, arising from the mandibular arch muscles and the bottom of the mouth, and are attached to the lower jaw and are innervated by trigeminal nerve (V couple). Of the muscles, the corresponding 2-nd gill arch, is mainly subcutaneous musculature of the neck and head, Inner viruemaya facial nerve (VII pair).

Muscles arising from the material of the two gill arches, have a double attachment, and a dual innervation, for example, digastric, anterior belly of which is attached to the mandible (innervation of the trigeminal nerve), and back - to the hyoid bone (innervation of the facial nerve). Visceral musculature, innervated by IX and X pairs of cranial nerves, in terrestrial vertebrates part is reduced, is part of the education of muscles of the pharynx and larynx. Trapezius muscle loses all connection with the gill arches and becomes extremely muscle upper extremity. In mammals split off from it in a separate part of the sternoclavicular-mastoid muscle. Posterior branch of the vagus nerve, Inner viruyuschaya trapezius muscle, becomes higher vertebrates in a separate cranial nerve - n. accessorius. Since the cranial in all its parts is still education, then it can not expect the development of muscles. Therefore, at the head occur only some remnants of muscles, formed from the head somites. Among them must include the eye muscles originate from the so-called prootic myotomes (innervation of III, IV and VI pairs of cranial nerves) (see Fig. 68).

Occipital myotomes, together with the front trunk myotomes usually formed by the ventral processes of particular podzhabernuyu or hyoid muscles lying under the visceral skeleton. At the expense of the muscles, penetrating to the anterior mandible, occur at the vertebrate tongue muscles, supplied with by virtue of descent from the occipital somites set of nerve fibers forming the hypoglossal nerve, which only in higher vertebrates has become a real cranial nerves. The rest of the hyoid muscles (below the hyoid bone) is a continuation of the ventral trunk muscles, innervated by the anterior branch of spinal nerves. Thus, to understand the location and fixation of the muscles must be considered, but their functions, and also development (see Fig. 66, 67).